windows xp home

Ok so I just got a new 40gb hd for my dell dimension 4300 that was given 2 me and when I put the windows disk in it start to load the os then gets so far and restarts. It says there's already an os on the hd even after several attempts at formatting the drive it says hit enter to install windows. I hit enter. And it says not to put the system on the hard drive because windows is already installed when I go into setup it says the hd has ogb of available space. I hope this makes sense its late and I've been doing this 4 3 hrs any help would be greatlt appreciated

 

In the original packaging new?

 

New as in from my uncle but there's nothing on it

 

Apparently, there is. Delete all partitions then run the install again after you go into BIOS and set the boot order to hard drive then CD.

http://support.dell.com/support/edocs/systems/dim4300/syssetup.htm#1097056